This invention relates to a method of culturing mammalian cells and, more particularly, to a method for rapidly adapting mammalian cell lines to growth in agitated liquid suspension culture.
The propagation of mammalian cells in agitated liquid suspension has been carried out in many laboratories. The earliest reported work is that of Owens et al, Ann. N.Y. Acad. Sci. 58, 1039-55 (1954) and Earle et al, J. Nat. Cancer Inst. 14,1159-71 (1954). Since that time, numerous cell lines have been adapted to suspension culture. Extensive reviews on this subject have been provided by Cherry and Hull, J. Biochem. Microbiol. Tech. Eng. II (3), 267-85 (1960), and by Moore and Ulrich, J. Surg. Res. 5 (6), 270-82 (1965).
Suspension culture of mammalian cells is desirable from the standpoint of large scale propagation of cells. This method of cell culture does not have any of the time and space limitations that are inherent with conventional monolayer growth. In the past, much attention has been given to the culture apparatus conditions and the nutrient media in attempting to develop practical suspension culture methods. Examples of these culture apparatus conditions and nutrient media are those such as disclosed by Earl et al, U.S. Pat. No. 2,990,335 and McLimans et al, U.S. Pat. No. 3,039,932, respectively. In most of the reported procedures, the cells are normally grown as a bulk suspension of discrete cells. Any transient aggregation of cells during the suspension culturing has been viewed as troublesome and conditions have been arranged to avoid or eliminate such aggregation; Cook et al, In Vitro 9, (5) 318-30 (1974) and U.S. Pat. No. 3,850,748.
It is also known that tumor cells can be grown as multi-cell spheroids in a non-agitated suspension of soft agar; Folkman and Hochberg, J. Expt'l Med. 138, 745-75 (1973). In other cases, individual tumor cells have been observed to aggregate over the surface of soft agar or to slough off the surface of soft agar and float in the medium; Costachel et al., Z. Krebsforsch 72, 24-31 (1969).
In contrast to these prior art methods of cell propagation in suspension culture, the present invention is concerned with the intentional employment of cell aggregates as means of rapidly adapting cell growth from substrate-attached culture to agitated liquid suspension.